The present invention relates generally to downhole oil well tools and, specifically, to an expendable plug assembly designed for use with a well packer, bridge plug, and the like.
Plug assemblies are typically installed within the bore of a well packer or other apparatus, usually at the lower end thereof, for location within a subterranean well at a predetermined depth. With the plug in place in the well bore, as within a set packer bore, a plurality of production zones can be isolated within the well for selective treatment of one or more of the zones.
When the first or upper zone of the well has been treated and the operator desires to either produce through the packer bore or treat the second or lower zone, a tube string is inserted within the well through the bore of the packer to disengage the plug assembly from the set well packer to thereby expend the plug from the packer bore. The plug assembly is then usually allowed to fall to the bottom of the well.
Prior plug assemblies used in operations of the type described have tended to be complex, expensive and difficult or time consuming to manufacture. Certain of the prior plug designs required that the plug be retrieved to the top of the well and the tubing or production string be reinserted into the well for subsequent treatment or production of additional zones. Other of the prior plug designs failed to balance the pressure differentials existing across the plug assembly so that a piston effect was created making it difficult to expend the plug from the bottom of the set well packer.
There exists a need, therefore, for an expendable plug assembly which is simple in construction and operation and relatively inexpensive to manufacture.
There also exists a need for a plug assembly which can be expended from the bore of a set well packer or other apparatus in a single trip so that the tubing utilized to expend the plug can also be utilized to produce or treat a second and lower zone in the well without the requirement of retrieval of the tubing subsequent to the operation of expending the plug.
There also exists a need for a plug assembly which is pressure balanced during the expending operation to facilitate removal of the plug from the packer bore.
There also exists a need for a plug assembly which can be installed within the packer bore in the field without the necessity of dissassembling the packer so that the packer tolerances are not affected prior to running the tool.